Conventional earth shoring systems and construction of permanent subterranean/underground structures evidence a number of limitations and inefficiencies. Previous construction industry methods incorporate a two-step process utilizing temporary lagged solder beams (cantilevered, rakered, or tie back supported), precast concrete (PCC) caissons, sheet piling, soil nailing, plate girders, or incrementally placed reinforced structural shotcrete to restrain the soil during excavation until a permanent structure can be built. Drilling, pile installation, lagging and the pile support system (required for deeper structures) are all temporary facilities/construction that are wasted following the construction of the permanent structure. Optimally, it would be advantageous if an underground structure could be built incorporating the temporary facilities/construction into the permanent structure.
Speaking generally, construction safety regulations and soil mechanics limit the vertical depth that an excavation can achieve without some form of soil support. Therefore, in the present industry, temporary shoring walls are typically erected so that excavation in preparation of underground construction is compliant with soil engineering practice and construction safety standards and laws. Thus, construction of a typical underground structure, such as an underground parking garage, requires that a contractor practically build an underground structure twice: (i) once to temporarily stabilize the excavation site, (e.g. temporary shoring walls), and (ii) a second time to erect the permanent structure.
Unfortunately, other inefficiencies are inherent existing methods, such as additional soil disturbance, excavation, and soil removal requirements allowing room for temporary shoring, which is constructed outside the newly constructed structure. Further, many times, the temporary shoring walls require additional structural support systems or members that physically obstruct or interfere with the permanent structures' construction.
In some existing applications, following the erection of a permanent structure, either part or all of the temporary shoring must be disassembled and removed. Following removal of the temporary shoring, the space between the earth and the permanent structure, now a deep void typically encircling the entire permanent structure, must be filled with additional soil or structural backfill. Other internal supports, as is the case of shoring utilizing rakers, must also be removed and their penetrations through the structure repaired.
As one can appreciate, the above described tasks relating to designing, erecting, dissembling, removing, patching, and back-filling temporary shoring walls command significant additional resources to be expended beyond the cost of erecting a permanent structure, and further compound the complex process of building a permanent underground structure. Further, the above described details require significant amounts of time and manpower to construct any temporary shoring systems which are not used in the permanent structure. This can be equated to significant lost, or wasted time and manpower.
Given the above constraints and problems, a new and efficient manner of constructing underground structures, alleviating the need for temporary shoring structures, would be advantageous. While an underground parking garage presents an exemplary case in point to demonstrate the need for a better solution, this need is felt on a broader level for many other applications requiring a cost effective, structurally sound, efficient underground structure.